Venable Richard M, Delaglio Frank, Norris Scott E, Freedberg Darón I
Laboratory of Biophysics, Center for Biologics Evaluation and Research, FDA, 1401 Rockville Pike, HFM-419, MD 20852, USA.
Carbohydr Res. 2005 Apr 11;340(5):863-74. doi: 10.1016/j.carres.2005.01.025.
The solution structure and dynamics of sucrose are examined using a combination of NMR residual dipolar coupling and molecular mechanics force fields. It is found that the alignment tensors of the individual rings are different, and that fitting 35 measured residual dipolar couplings to structures with specific phi, psi values indicates the presence of three major conformations: phi, psi=(120 degrees ,270 degrees), (45 degrees, 300 degrees) and (90 degrees ,180 degrees). Furthermore, fitting two structures simultaneously to the 35 residual dipolar couplings results in a substantial improvement in the fits. The existence of multiple conformations having similar stabilities is a strong indication of motion, due to the interconversion among these states. Results from four molecular mechanics force fields are in general agreement with the experimental results. However, there are major disagreements between force fields. Because fits of residual dipolar couplings to structures are dependent on the force field used to calculate the structures, multiple force fields were used to interpret NMR data. It is demonstrated that the pucker of the fructofuranosyl ring affects the calculated potential energy surface, and the fit to the residual dipolar couplings data. Previously published 13C nuclear relaxation results suggesting that sucrose is rigid are not inconsistent with the present results when motional timescales are considered.
利用核磁共振剩余偶极耦合和分子力学力场相结合的方法，研究了蔗糖的溶液结构和动力学。研究发现，各个环的取向张量不同，将35个测得的剩余偶极耦合拟合到具有特定φ、ψ值的结构上，表明存在三种主要构象：φ、ψ =（120度，270度）、（45度，300度）和（90度，180度）。此外，将两种结构同时拟合到35个剩余偶极耦合上，拟合效果有显著改善。由于这些状态之间的相互转换，存在多个具有相似稳定性的构象是运动的有力指征。四个分子力学力场的结果总体上与实验结果一致。然而，力场之间存在重大分歧。由于将剩余偶极耦合拟合到结构上依赖于用于计算结构的力场，因此使用了多个力场来解释核磁共振数据。结果表明，呋喃果糖环的褶皱会影响计算出的势能面以及与剩余偶极耦合数据的拟合。当考虑运动时间尺度时，先前发表的表明蔗糖是刚性的13C核弛豫结果与目前的结果并不矛盾。
